Constrained Order Observer Design for Disturbance Decoupled Output Estimation

From industry there is an increasing interest in applying model based control techniques to large-scale systems. Control designs like H
₂
and H
_∞
optimal control will typically contain a dynamic state observer in which the order will be equal to the model order. Consequently, real-time implementation of the controller may not be possible due to computational constraints. The problem of designing a constrained order observer for a large-scale system, with explicit guarantees on the output estimate is therefore a relevant problem in these applications. This letter addresses the problem of constructing (if it exists) an observer with a constrained order that decouples the output estimation errors from the disturbances that are acting on the system. In addition, stability of the output estimate, a characterization of the orders for which the observer can achieve disturbance decoupled estimation and the explicit construction of the observer are discussed.